Apparatus and method for directional drilling of holes

ABSTRACT

An apparatus for the directional drilling of bore hole through a solid substrate includes a main bore head mounted for rotation on a flexible drive shaft and a pilot bore head for weakening a region of substrate in advance of the main bore head, the weakened region being eccentrically located relative to the main bore head. The apparatus further includes structure for enabling the drilling access of the main bore head, during subsequent drilling of the bore hole, to become substantially aligned with the weakened region of substrate.

This invention relates to an apparatus and method of drilling holes inmasonry or any other suitable material using a cutting head, or asimilar means of excavating the material, where the route of the cuttinghead can be adjusted during the cutting process to follow a variablepath.

Directional drilling tools have been developed in recent years to enablethe trenchless installation of underground utility lines.

One such tool is disclosed in U.S. Pat. No. 5,490,569. This apparatuscomprises a circular drill bit which is mounted for rotation on a driveshaft. Downstream from the bore head, the drive shaft is housed in anaxial hollow formed within a circular casing which extends substantiallyalong the entire axial length of the drilled hole. The radius of thecircular casing is nominally equal to or less than that of the cuttingcircle of the drill bit. A deflection shoe is mounted on the externalwall of the casing at a position close to the drill bit. The deflectionshoe extends radially outward from the casing and engages with the wallof the drilled hole. At least a portion of the deflection shoe liesoutside the cutting circle of the drill bit and, as drilling progresses,the drill bit is deflected in a direction opposing that in which thedeflection shoe extends from the casing. Rotation of the casing willcause a change in the direction of deflection of the drill bit.Continuous rotation of the casing will enable to operator to drillstraight ahead.

A further directional drilling tool is disclosed in U.S. Pat. No.5,421,421. This document teaches that as an alternative to employing apermanently mounted deflection shoe, retractable steering plungers maybe extended from the casing when a deflection of the drill bit path isdesired and retracted to enable the drill bit to proceed in a straightline. The plungers are activated by hydraulic pressure which is suppliedfrom a fluid control means which increases the complexity and cost ofthe tool.

In accordance with the present invention, there is provided an apparatusfor the directional drilling of a bore hole through a solid substrate,the apparatus including:

a main bore head mounted for rotation on a flexible drive shaft;

means for weakening a region of substrate in advance of the main borehead, the weakened region being eccentrically located relative to themain bore head; and

means for enabling the drilling axis of the main bore head, duringsubsequent drilling of the bore hole, to become substantially alignedwith the weakened region of substrate.

Preferably the means for weakening a region of substrate includes apilot bore head mounted for rotation on a flexible pilot drive shaftpassing eccentrically through the main bore head. Preferably means areprovided for advancing the pilot bore head from the main bore head tocreate a pilot bore in the substrate and for retracting the pilot borehead into the main bore head after creation of the pilot bore, the pilotbore defining the weakened region of substrate. The means for enablingthe drilling axis of the main bore head to become substantially alignedwith the weakened region of substrate preferably comprises means forenabling the drilling axis of the main bore head to become substantiallyaligned with the axis of the pilot bore drilled by the pilot bore head.

Preferably the main bore head includes a drilling point which definesthe drilling axis of the main bore head. Preferably the axis of thepilot bore is axially offset from this drilling point. The axial offsetmay represent less than about 25% of the diameter of the main bore head.The axial offset may be sufficiently small that the main bore head will,during drilling, find its own way into the pilot bore.

Preferably the drilling point of the main bore head is eccentricallypositioned relative to the bore head. The drilling point may bepositioned between a quarter and a third of the way along a diameter ofthe bore head. Preferably the drilling point and the pilot bore head arepositioned within respectively the same half of the main bore head. Thedrilling point and the pilot bore head may be located generally on thesame radius of the main bore head. The pilot bore head is preferablylocated outwardly of the drilling point of the main bore head.

Rotation of the eccentric bore head may form a bore hole of sufficientlylarge diameter that the drilling point of the bore head may move intoalignment with the bore hole, without the need to drill away any furthersubstrate.

The apparatus may further include means for moving the main bore head,to position its drilling axis substantially on the axis of the pilotbore drilled by the pilot bore head. These means may include means forextending from an outer circumference of the main bore head at aposition generally on an opposite side of the main bore head to thedrilling point. The extending means may be substantially diametricallyopposed to the drilling point. The extending means may include anextensible and retractable cam. The cam may be biased into its extendedposition. The cam may be mounted such that, when the main bore head isrotated in a drilling direction, the cam is urged against the force ofthe biasing means into its retracted position. The cam may be mountedsuch that, when the bore head is rotated in an opposite direction, thecam is urged by the biasing means against an inner surface of the mainbore hole, to push the main bore head away from that surface.

Preferably the pilot bore head is mounted within the main bore head suchthat relative rotation therebetween may be selectively allowed orprevented. Means may be provided for allowing such relative rotationwhen the pilot bore head is in its advanced position and preventing suchrelative rotation when the pilot bore head is in its retracted position.The means for preventing relative rotation may include a plurality oflocking splines.

The axis of the pilot bore head may be substantially parallel to theaxis of the main bore head. Alternatively the axis of the pilot borehead may be angled at up to about 45° from the axis of the main borehead.

In accordance with the present invention, there is further provided anapparatus for the directional drilling of a bore hole through a solidsubstrate, the apparatus including:

a main bore head rotatably mounted on a flexible main drive shaft;

a pilot bore head rotatably mounted on a flexible pilot drive shaftpassing eccentrically through the main bore head;

means for advancing the pilot bore head from the main bore head tocreate a pilot bore in the substrate;

means for retracting the pilot bore head into the main bore head aftercreation of the pilot bore; and

means for allowing the drilling axis of the main bore head, duringsubsequent drilling of the bore hole, to become substantially alignedwith the axis of the pilot bore drilled by the pilot bore head.

In accordance with a further aspect of the present invention, there isprovided an apparatus for the directional drilling of a bore holethrough a solid substrate, the apparatus including:

a main bore head rotatably mounted on a flexible main drive shaft;

a pilot bore head rotatably mounted on a flexible pilot drive shaftpassing eccentrically through the main bore head;

means for advancing the pilot bore head from the main bore head tocreate a pilot bore in the substrate; and

means for rotating the main bore head, with the pilot bore head locatedin the pilot bore, to laterally alter the position of the main bore headwithin the substrate.

According to a further aspect of the present invention there is providedan apparatus for the directional drilling of a bore hole through a solidsubstrate, the apparatus including:

a main bore head mounted for rotation on a flexible main drive shaft;and

an extensible and retractable cam, the cam being biased into itsextended position and mounted such that, when the main bore head isrotated in a drilling direction, the cam is urged against the force ofthe biasing means into its retracted position and when the bore head isrotated in an opposite direction, the cam is urged by the biasing meansagainst an inner surface of the main bore hole, to push the main borehead away from that surface.

In accordance with a further aspect of the present invention, there isprovided an apparatus for the directional drilling of a bore holethrough a solid substrate, the apparatus including:

a main bore head mounted for rotation on a flexible main drive shaft;and

elongate tensioning means extending axially along the flexible driveshaft substantially from the main bore head end of the drive shafttowards a driven end of the drive shaft, wherein tension in thetensioning means tends to urge the flexible drive shaft to bend, therebyaltering the drilling direction.

Preferably the elongate tensioning means is anchored at a positionremote from the main bore head, extends towards the main bore head,passing freely through a locating means, and then extends towards thedriven end of the drive shaft.

Preferably the elongate tensioning means comprises a wire.

According to the invention, there is further provided apparatus for thedirectional drilling of a bore hole through a solid substrate, theapparatus including:

a main bore head;

a pilot bore head mounted for rotation on a flexible shaft; and

means for exerting a force on the main bore head when it is located in abore hole, to urge the bore head towards one side of the bore hole.

The main bore head and the pilot bore head may be mounted onrespectively the same shaft or on different shafts.

The biasing means may include an extensible and retractable cam. The cammay be located on the main bore head. Alternatively the cam may belocated on the main drive shaft. Preferably the cam is biased into theretracted position. The cam may be extended or retracted by applyingtension to a cable connected to the cam and extending to a non-drillingregion of the drilling apparatus.

The apparatus may further include one or more additional bore heads,between the main bore head and the pilot bore head in size.

The apparatus may further include means for conveying a lubricant, forexample water to the or each bore head, for lubricating the drillingprocess.

The pilot shaft and the main bore shaft may be in threaded engagementwith one another.

According to the invention there is further provided a method for thedirectional drilling of a bore hole through a solid substrate, themethod including the steps of:

drilling a main bore hole using a main bore head;

weakening a region of substrate in advance of the main bore head, theweakened region being eccentrically located relative to the main borehead; and

drilling further with the main bore head, allowing the axis of the mainbore head to become aligned with the weakened region in the substrate.

According to the invention there is further provided a method for thedirectional drilling of a bore hole through a solid substrate, themethod including the steps of:

drilling a main bore hole using a main bore head;

drilling a pilot bore hole in the substrate at an end of the main borehole, the pilot bore hole having an axis offset from a drilling axis ofthe main bore head; and

drilling further with the main bore head, allowing the axis of the mainbore head to become aligned with the axis of the pilot bore hole suchthat the main bore hole follows the path of the pilot bore hole.

The drilling of the pilot bore hole may weaken the substrate at the endof the main bore hole, in a region between the pilot bore hole and thedrilling axis of the main bore head.

The method may include the step of moving the main bore head intoalignment with the pilot bore hole, before or during the furtherdrilling with the main bore head.

Embodiments of the invention will be described for the purpose ofillustration only with reference to the accompanying drawings, in which:

FIG. 1 is a schematic cross-sectional view of a drilling tool inaccordance with a first embodiment of the present invention;

FIG. 2 is a schematic cross-sectional view of a drilling tool inaccordance with a second embodiment of the present invention;

FIG. 3 is a schematic view of the drilling tool of FIG. 1 at a firstinstant in time;

FIG. 4 is a schematic view of the drilling tool of FIG. 1 at a secondinstant in time;

FIG. 5 is a schematic view of the drilling tool of FIG. 1 at a thirdinstant in time;

FIG. 6 is a schematic view of the drilling tool of FIG. 1 at a fourthinstant in time;

FIG. 7 is a schematic view of the drilling tool of FIG. 1 at a fifthinstant in time;

FIG. 8 is a schematic end view of the drilling tool of FIG. 1 with apressure cam in a retracted position;

FIG. 9 is a schematic end view of the drilling tool of FIG. 1 with thepressure cam in an extended position;

FIG. 10 is a partial schematic side view of a drilling tool inaccordance with a third embodiment of the present invention;

FIG. 11 is a partial schematic side view of a drilling tool inaccordance with a fourth embodiment of the present invention;

FIG. 12 is a partial schematic side view of a drilling tool inaccordance with a fifth embodiment of the present invention;

FIG. 13 is a partial schematic side view of a drilling tool inaccordance with a sixth embodiment of the present invention;

FIGS. 14A and 14B are a partial schematic side view and a detail thereofof a drilling tool in accordance with a seventh embodiment of thepresent invention;

FIGS. 15A and 15B are a partial schematic side view and a detail thereofof a drilling tool in accordance with an eighth embodiment of thepresent invention; and

FIG. 16 is a partial schematic side view of a drilling tool inaccordance with a ninth embodiment of the present invention.

As shown in FIG. 1, directional drilling apparatus in the form of adrilling tool 1 includes a main drilling bore head 2 and a pilotdrilling bore head 4. The main drilling bore head 2 has a drilling point6 which is displaced laterally from the centre axis XX of the maindrilling bore head 2. A pressure cam 12 is mounted on the side of themain drilling bore head 2 and is positioned to act at the furthest pointfrom the drilling point 6.

The pilot drilling bore head 4 has a pilot drilling axis YY and isreceivable within a hole in the main drilling bore head 2 such that thepilot drilling axis YY is displaced laterally from both the centre axisXX of the main drilling bore head 2 and the drilling point 6. The pilotdrilling bore head 4 is retractable through the main drilling bore head2 and is shown in an extended position SA, and ghosted a first retractedposition 5B and a second retracted position 5C.

The pilot drilling bore head 4 is mounted on a flexible drive shaft 8which passes through the hole in the main drilling bore head 2. Theflexible drive shaft 8 is contained within another flexible drive shaft10 which is used to drive the main drilling bore head 2.

The pilot drilling bore head 4 includes locking splines 13 which areused to lock the pilot drilling bore head 4 to the main drilling borehead 2 when the pilot drilling bore head 4 is in the second retractedposition 5C. The locking splines 13 are disengaged when the pilotdrilling bore head 4 is extended to the first retracted position 5Ballowing the pilot drilling bore head 4 to be driven by the flexibledrive shaft 8 in this position.

The pilot drilling axis YY of the pilot drilling bore head 4 does notnecessarily have to be parallel with the centre axis XX of the maindrilling bore head 2 but may instead be positioned at a fixed angle tothe centre axis XX of the main drilling bore head 2 as shown in FIG. 2.

The operation of the drilling tool 1 as shown in FIG. 1 is now explainedwith reference to FIGS. 3 to 7. The drilling tool 1 is shown within amain bore 14 which is wider than the main drilling bore head 2. Asexplained later in more detail this is because the drilling point 6 ofthe main drilling bore head 2 is laterally displaced from the centreaxis XX of the main drilling bore head 2.

Initially, the pilot drilling bore head 4 is angularly positioned byrotating the main drilling bore head 2. The pilot drilling bore head 4is then extended as shown by the arrow AA until the locking splines 13of FIG. 1 are disengaged and the pilot drilling bore head 4 is no longersecured to the main drilling bore head 2. The pilot drilling bore head 2is then rotatably driven by the flexible drive shaft 8 of FIG. 1 and isadvanced into a section of the masonry 16.

Once the pilot drilling bore head 4 has been advanced a predetermineddistance the pilot drilling bore head 4 is retracted into the maindrilling bore head 2 until the locking splines 13 of FIG. 1 secure thepilot drilling bore head 4 to the main drilling bore head 2. The pilotdrilling bore head 4 leaves behind a pilot bore 18 having a diameter thesame as that of the pilot drilling bore head 4. The drilling of thepilot bore 18 creates an area of weakened masonry 20 between the pilotbore 18 and the drilling point 6 of the main drilling bore head 2.

Once the pilot drilling bore head 4 is secured to the main drilling borehead 2 the main drilling bore head 2 is then rotatably driven by theflexible drive shaft 10 of FIG. 1 and is advanced as shown by the arrowBB. The weakened area of masonry 20 is easier to drill than thesurrounding masonry and as the main drilling bore head 2 is advanced itmoves toward the pilot bore 18 as shown by the arrow CC.

During drilling, the drilling point 6 of the main drilling bore head 2acts as a rotation axis around which the main drilling bore head 2rotates. Because the drilling point 6 (and hence the rotation axis) ofthe main drilling bore head 2 is laterally displaced from the centreaxis XX of the main drilling bore head 2 the main drilling bore head 2rotates eccentrically about the drilling point 6 and the resulting mainbore 14 has a diameter larger than that of the main drilling bore head2.

Once the drilling point 6 of the main drilling bore head 2 is positionedwithin the pilot bore 18 drilling continues, centred on the pilot bore18, until the main drilling bore head 2 has advanced a predetermineddistance. The new main bore 22 is laterally displaced from the previousmain bore 14 by a distance DD as shown.

Finally, the pilot drilling bore head 4 is angularly repositioned byrotating the main drilling bore head 2 and the drilling sequence beginsagain. In this way the main drilling bore head 2 and the resulting mainbore is laterally “stepped” through the masonry.

If the pilot drilling axis YY is not parallel to the centre axis XX ofthe main drilling bore head 2 illustrated in FIG. 2 then the resultingpilot hole will angle the main drilling axis of the main drilling borehead 2 as it advances with the drilling point 6 centred on the pilothole. In this way the main drilling bore head 2 and the resulting mainbore can be made to follow a smooth curved route instead of the“stepped” route described above.

The pressure cam 12 may also be used if the main bore is to follow acontinuous curved path or if other adjustments are necessary whichcannot be accomplished by using either of the methods described above.The operation of the pressure cam 12 is now explained with reference toFIGS. 8 and 9.

The pressure cam 12 is mounted on the side of the main drilling borehead 2 and is receivable within the main drilling bore head 2 when in aretracted position 24A The pressure cam 12 includes a cam tensioningspring 28 which acts to keep the pressure cam 12 in an extended position24B. The pressure cam 12 is positioned to be at the furthest point fromthe drilling point 6 of the main drilling bore head 2 around which themain drilling bore head 2 rotates during operation. This means that thepressure cam 12 is in contact with the inner surface of the main bore 26at all times. When the main drilling bore head 2 is stationary orrotating in a cutting direction CW the saw-tooth shape of the pressurecam 12 means that it is kept in the retracted position 24A by the innersurface of the main bore 26.

Activation and deactivation of the pressure cam is achieved by reversingthe direction of rotation of the main drilling bore head 2. When themain drilling bore head 2 is rotated in a direction opposite to thecutting direction ACW then the friction between the pressure cam 12 andthe inner surface of the main bore 26 due to the saw-tooth shape of thepressure cam 12, and the additional force exerted by the cam tensioningspring 24, means that the pressure cam 12 is activated and pivotsoutwards. The pressure cam 12 exerts a radial force on the inner surfaceof the main bore 26 and causes the main drilling bore head 2 to moveaway from that side of the main bore 26. Further changes in directionmay be made by alternately activating and deactivating the pressure cam12 to steer the main drilling bore head 2.

The drilling tool 1 may be used in, for example, the reinforcement ofcurved structures such as arched bridges. An operator may use thedrilling tool 1 to drill a curved or stepped hole generally in line withthe shape of the bridge. Marks in the form of lines extending along thedrive shaft to its driven end may indicate the circumferential positionsof the pilot bore and the cam, to enable the operator to adjust the pathof the drilling tool as required.

The path of the drilling tool may be monitored by drilling small pilotholes into the structure, substantially transverse to the drillingdirection.

Once a suitable main bore hole has been drilled, a reinforcement bar maybe inserted. The reinforcement is preferably of metal but is of asufficiently narrow diameter that it may bend to follow the path of thecurved hole. The bar may be grouted into place by injecting grout fromthe base of the hole. When grout starts to flow out of the first pilothole, this indicates that the main bore hole is filled with grout atleast to the point where it meets that pilot hole. The end of that pilothole is then sealed and the injection of grout continued until it startsto flow out of the next pilot hole. This process is continued until allthe pilot holes, and also thus the full length of the main bore hole,are full of grout.

There is thus provided a drilling tool and method of drilling which maybe used to drill stepped, angled or generally curved bores in masonry.The operation of the tool is relatively straightforward in comparisonwith prior art methods. The tool is particularly useful for thereinforcement of bridges in accordance with the Applicant's EuropeanPatent No. 2302896.

Various modifications may be made to the above described embodimentwithout departing from the scope of the invention. The dimensions of theapparatus will of course depend upon its application. The flexible driveshaft is likely to be between 15 mm and 100 mm in diameter, with thediameter of the main drilling bore head being in a similar range buttypically about twice the diameter of the drive shaft. The diameter ofthe pilot shaft is likely to be between 5 mm and 20 mm.

A pilot bore need not be used for weakening the substrate. Other meansfor weakening the substrate might include, for example, directing a jetof water at the region of substrate to be weakened.

Instead of allowing main bore head to locate itself in alignment withthe weakened region or the pilot bore hole, the pilot bore may be leftwithin the pilot bore hole and the main bore head rotated with the pilotbore in place. This forces the main bore head to shift its axis towardsthat of the pilot bore.

Alternatively, the cam alone may be used to shift the axis of the mainbore head. Where the substrate is relatively weak, there may not be anyneed to use the pilot bore.

Instead of being located on the main bore head, the cam may be locatedon the drive shaft, near the main bore head. Cams could be provided bothon the main bore head and on the drive shaft.

Alternatively, the direction of drilling may be controlled asillustrated in FIG. 10. According to this embodiment of the invention,the flexible drive shaft 10 is provided with a tension wire 30 foradjusting the drilling direction. The tension wire 30 is attached to thedrive shaft 10 at a point 32 spaced from the drilling end 34 of thedrive shaft 10. The tension wire 30 then extends towards the drillingend 34 of the drive shaft and passes freely through a guide 36, doublingback on itself to extend to the drive end of the drive shaft 10. Thewire 30 passes through further guides (not illustrated) to ensure thatit does not move around the circumference of the drive shaft.

In the above embodiment, the tension wire 30 may be pulled to adjust theorientation of the drive shaft. The wire 30 may be provided on an outersleeve 40 which is freely rotatable relative to the drive shaft 10. Theouter sleeve 40 may be rotated to a desired orientation and the wire 30pulled to bend the drive shaft in a particular direction duringdrilling.

In any of the above described embodiments, an outer sleeve may be usedto assist the passage of the drilling tool into the substrate. An outersleeve or shaft could surround the shaft 10 and be in threadedengagement therewith. The outer shaft could then be prevented fromrotating while the shaft 10 rotates, this causing relative axialmovement therebetween. This could be used to force the shaft 10 into asubstrate and would be particularly useful where hard substrates wereinvolved.

FIG. 11 illustrates a further embodiment of the invention. A directionaldrilling apparatus in the form of a drilling tool 1 includes a pilotbore head in the form of a drilling head 28 mounted on a flexible, innerdrive shaft 30. The drilling tool 1 further includes main bore heads inthe form of drilling heads 32, 34 and 36.

Typically, the pilot drilling head 28 may be 15 mm in diameter, with across sectional area of about 180 mm². A second stage drilling head 32may then be about 30 mm in diameter and the subsequent drilling heads ofa larger diameter.

The drilling heads in this embodiment have flat faces and includediamonds set in resin welded to the faces in a desired pattern tooptimise drilling performance.

An outer flexible drive shaft 38 surrounds and is co-axial with theinner drive shaft. Mounted on the outer flexible drive shaft 38 is aretractable steering cam 40, the function of which is described below.

Each of the drilling heads 28, 32, 34 and 36 may be selectively fittedto the inner drive shaft one at a time or together by use of pins,threaded connections, keyed collars, clamping a chuck or jaws. Suchmethods are known to the person skilled in the art and are notillustrated in FIG. 11.

In use, the pilot drilling head 28 is initially coupled to the innerdrive shaft 30 and rotated in order to drill a small pilot bore. It isdesirable initially to use a small diameter pilot drill because alldrills have a “dead spot” in the centre whether the drill spins onitself and does not cut. With a pilot drill of small diameter, this deadspot is relatively small.

Once the pilot drill hole has been created, the further drilling headsmay be coupled together or one at a time to the inner drive shaft 30 andused to drill the hole until it is of sufficient size.

The main drilling heads 32, 34 and 36 may then be removed before thenext pilot hole is created. At this time, the cam 40 may be used tosteer the drilling tool 1. Once the main drilling heads have beenremoved, the drilling tool 1 is located in a bore which has a diametergreater than that of the drilling tool. The retractable cam 40 maytherefore be extended in order to push the drilling tool 1 in a chosendirection within the bore. The outer flexible drive shaft 30 may berotated to a desired position, with the cam located opposite to thechosen direction of travel for the drilling tool 1. The cam 40 may thenbe extended, for example by a cam piston or pressure plate activated byair, gas, fluid, etc. This therefore pushes the drilling tool 1 towardsa chosen side of the bore. The inner drive shaft may then be rotated toactivate the pilot drill, with the cam still extended and in engagementwith the inside of the bore hole. The cam therefore forces the pilotdrill to create a bore hole which is located eccentrically relative tothe axis of the previously drilled larger bore. The above describedprocess may then be repeated, and the drilling tool 1 may thus be usedto drill in any chosen direction.

In the above embodiment, the cam 40 may alternatively be operated withthe main drilling heads in place. In this case, it produces a biasingforce urging the drilling tool in a particular direction within thebore. In the above described embodiment in which the main drilling headsare selectively couplable to the inner drive shaft 30, the outer shaftmay only rotate to move and actuate the cam 40. However, in analternative embodiment, one or more of the main drilling heads 32, 34,36 may be couplable to the outer drive shaft 38, which would then berotated to effect the drilling operation.

FIG. 12 illustrates a drilling tool according to a further embodiment ofthe invention. In this embodiment, a pilot drilling head 28 and maindrilling heads 32 and 34 are selectively couplable to an inner driveshaft 30. A large drilling head 36 is coupled to an intermediate driveshaft 42 located outwardly and coaxially with the inner drive shaft 30.An outer flexible drive shaft 38 surrounds the intermediate drive shaft42.

In the above embodiment, a retractable steering cam 44 is mounted on thelarge drilling head 36. The cam may be activated or de-activateddependent on the direction of rotation of the intermediate drive shaft42, as described above in relation to the embodiment of FIGS. 1 to 9.This embodiment operates generally similarly to the embodiment of FIG.11 above except that the rotation of the large drilling head 36 is usedto effect the changes in direction of the drilling tool 1.

FIG. 13 illustrates a further embodiment of the invention, which isgenerally similar to that of FIG. 12 except that a pipe 44 is providedfor providing water to lubricate the drill head and remove debris. Thepipe is located within the inner drive shaft 30, co-axial therewith, andconveys water to a water injection point 46 on the pilot drilling head28.

The embodiments of FIGS. 14A and 14B again includes a pilot drillinghead 28 mounted on an inner drive shaft 30 and a larger drilling head 32mounted on an intermediate drive shaft 42. A steering plate 48 iscoupled to an outer flexible drive shaft 38.

The steering plate 48 includes on each of two diametrically opposedsides a cam 50 which is normally biased by a spring 52 into a position(illustrated in FIG. 14A) where it does not project beyond the outerdiameter of the drilling head 32. Referring to the detail in FIG. 14B, atension cable 54, which extends down the axis of the drilling toolinternally of the outer flexible drive shaft 38 may be pulled toovercome the bias of the spring 52 and force the cam into the positionshown in FIG. 14B. In such position, the cam 50 forces the drilling tool1 to move away from the side 56 of the drilled hole. The steering plateand cam may thus be used to control the direction of drilling.

The inner and intermediate drive shafts 30 and 42 may be in threadedengagement with the outer drive shaft 38. Thus, if the outer drive shaftis held in position, rotation of the pilot drilling head 28 or thedrilling head 32 forces the drilling head forward relative to the outerflexible drive shaft 38 and thus assists in the forward movement of thedrilling head.

The embodiment of FIGS. 15A and 15B is generally similar to that ofFIGS. 14A and 14B except that the tension cable 54 is located outsidethe outer flexible drive shaft 38.

The embodiment of FIG. 16 includes a pilot drilling head 28 mounted onan inner drive shaft 30 which is in threaded engagement with an outerdrive shaft 38. A main drilling head 32 is mounted on the outer driveshaft. A cam 40 is mounted on the main drilling head 32 but is inactivewhen the main drilling head rotates in a drilling direction. In thisembodiment, the pilot drilling head 28 may be used to drill a pilotbore, with the outer drive shaft held stationary and with the cam inengagement with an inner wall of the bore. The threaded engagementbetween the inner and outer drive shafts ensures that as the pilotdrilling head is rotated it is pushed forward relative to the outerdrive shaft and the main drilling head 32. Since the cam 40 engages theinner wall of the bore, this prevents backward movement of the outerdrive shaft 38 and forces the pilot drilling head 28 forward.

In any of the above embodiments, vibration may be used to assist thedrill head to move forward. The apparatus could include a non-cuttinghead functioning as an excavating device, for removal material to letthe drilling heads move forward. Such a non-cutting head might contain ahigh pressure water jet, air, electricity, reciprocating needles,rotating members, etc.

Means for rotating the flexible drive shafts is provided at thenon-drilling ends of the shafts. These means include a main drive motorwhich causes the shafts to rotate as desired and which also may push achosen drive shaft through a tube which guides it to the structure to bedrilled. This ensures that the shafts are contained and pass correctlyinto the drilled hole. The motor may also push the shaft forwards withinthe bore. A pump may also be provided to convey water or anotherlubricant to the drill heads and wires or tubes may be provided whichare connected to the drill head to operate the steering mechanisms. Thewires or tubes may be connected to levers on or near the drill head toexert additional pressure to push the drill head forward. Thisadditional forward pressure is particularly useful as the drill headmoves further away from the drilling rig.

Whilst endeavouring in the foregoing specification to draw attention tothose features of the invention believed to be of particular importanceit should be understood that the Applicant claims protection in respectof any patentable feature or combination of features hereinbeforereferred to and/or shown in the drawings whether or not particularemphasis has been placed thereon.

1. Apparatus for the directional drilling of a bore hole through a solidsubstrate, the apparatus including: a main bore head mounted forrotation on a flexible drive shaft; means for weakening a region ofsubstrate in advance of the main bore head to create a pilot bore in thesubstrate, the weakened region being eccentrically located relative tothe main bore head; and means for enabling the drilling axis of the mainbore head, during subsequent drilling of the bore hole, to becomesubstantially aligned with the weakened region of substrate; and whereinthe main bore head includes a drilling point which defines the drillingaxis of the main bore head and the axis of the pilot bore is axiallyoffset from this drilling point.
 2. Apparatus according to claim 1,wherein the means for weakening a region of substrate includes a pilotbore head mounted for rotation on a flexible pilot drive shaft passingthrough the main bore head.
 3. Apparatus according to claim 2, whereinthe pilot bore head passes eccentrically through the main bore head. 4.Apparatus according to claim 1, wherein means are provided for advancingthe pilot bore head from the main bore head to create a pilot bore inthe substrate, the pilot bore defining the weakened region of substrate.5. Apparatus according to claim 1, wherein the means for enabling thedrilling axis of the main bore head to become substantially aligned withthe weakened region of substrate comprises means for enabling thedrilling axis of the main bore head to become substantially aligned withthe axis of the pilot bore drilled by the pilot bore head.
 6. Apparatusaccording to claim 1, wherein the drilling point of the main bore headis eccentrically positioned relative to the bore head.
 7. Apparatusaccording to claim 6, wherein the drilling point is positioned between aquarter and a third of the way along a diameter of the bore head, andthe drilling point and the pilot bore head are positioned withinrespectively the same half of the main bore head.
 8. Apparatus accordingto claim 1, wherein the apparatus further includes an extensible andretractable cam for moving the main bore head, to position its drillingaxis substantially on the axis of the pilot bore drilled by the pilotbore head, the cam extending from an outer circumference of the mainbore head.
 9. Apparatus according to claim 8, wherein the cam is biasedinto its extended position and mounted such that, when the main borehead is rotated in a drilling direction, the cam is urged against theforce of the biasing means into its retracted position, and when thebore head is rotated in an opposite direction, the cam is urged by thebiasing means against an inner surface of the main bore hole, to pushthe main bore head away from that surface.
 10. Apparatus according toclaim 1, wherein the pilot bore head is mounted within the main borehead such that relative rotation therebetween may be selectively allowedor prevented, and wherein means are provided for allowing relativerotation when the pilot bore head is in its advanced position andpreventing relative rotation when the pilot bore head is in itsretracted position.
 11. Apparatus for the directional drilling of a borehole through a solid substrate, the apparatus including a main bore headmounted for rotation on a flexible main drive shaft; a pilot bore headmounted for rotation on a flexible pilot drive shaft passingeccentrically through the main bore head; means for advancing the pilotbore head from the main bore head to create a pilot bore in thesubstrate; means for retracting the pilot bore head into the main borehead after creation of the pilot bore; and means for allowing thedrilling axis of the main bore head, during subsequent drilling of thebore hole, to become substantially aligned with the axis of the pilotbore drilled by the pilot bore head; and wherein the main bore headincludes a drilling point which defines the drilling axis of the mainbore head and the axis of the pilot bore is axially offset from thisdrilling point.
 12. Apparatus for the directional drilling of a borehole through a solid substrate, the apparatus including: a main borehead mounted for rotation on a flexible main drive shaft; a pilot borehead mounted for rotation on a flexible pilot drive shaft passingeccentrically through the main bore head; means for advancing the pilotbore head from the main bore head to create a pilot bore in thesubstrate; and means for rotating the main bore head, with the pilotbore head located in the pilot bore, to laterally alter the position ofthe main bore head within the substrate; and wherein the main bore headincludes a drilling point which defines the drilling axis of the mainbore head and the axis of the pilot bore is axially offset from thisdrilling point.
 13. Apparatus for the directional drilling of a borehole through a solid substrate, the apparatus including: a main borehead mounted for rotation on a flexible main drive shaft; and anextensible and retractable cam, the cam being biased into its extendedposition and mounted such that, when the main bore head is rotated in adrilling direction, the cam is urged against the force of the biasingmeans into its retracted position and when the bore head is rotated inan opposite direction, the cam is urged by the biasing means against aninner surface of the main bore hole, to push the main bore head awayfrom that surface.
 14. Apparatus for the directional drilling of a borehole through a solid substrate, the apparatus including: a main borehead; a pilot bore head mounted for rotation on a flexible shaft; andmeans for exerting a force on the main bore head when it is located in abore hole, to urge the bore head towards one side of the bore hole; andwherein the means for exerting a force includes an extensible andretractable cam located on the main bore head or on the main driveshaft, the cam being biased into a retracted position and beingengageable with the inside of the bore hole when in an extendedposition.
 15. Apparatus according to claim 14, wherein the main borehead is mounted for rotation on a flexible main drive shaft whichsurrounds the shaft on which the pilot bore head is mounted. 16.Apparatus according to claim 14, wherein the cam may be extended orretracted by applying tension to a cable connected to the cam andextending to a non-drilling region of the drilling apparatus. 17.Apparatus according to claim 16, the apparatus further including one ormore additional bore heads, between the main bore head and the pilotbore head in size.
 18. Apparatus according to claim 17, wherein thepilot shaft and the main bore shaft are in threaded engagement with oneanother.
 19. A method for the directional drilling of a bare holethrough a solid substrate, method including the steps of: drilling amain bore hole using a main bore head having a drilling point whichdefines a drilling axis of the main bore head; weakening a region ofsubstrate in advance of the main bore head by drilling a pilot borehaving an axis axially offset from the drilling point of the main borehead, the weakened region being eccentrically located relative to themain bore head; and drilling further with the main bore head, allowingthe axis of the main bore head to become aligned with the weakenedregion in the substrate.
 20. A method for the directional drilling of abore hole through a solid substrate, the method including the steps of:drilling a main bore hole using a main bore head having a drilling pointwhich defines a drilling axis of the main bore head; drilling a pilotbore hole in the substrate at an end of the main bore hole, the pilotbore hole having an axis axially offset from the drilling point of themain bore head; and drilling further with the main bore head, allowingthe axis of the main bore head to become aligned with the axis of thepilot bore hole such that the main bore hole follows the path of thepilot bore hole.